This invention relates to a power driven apparatus for rapidly driving fasteners such as screws or the like; hereafter the apparatus will be referred to as a "driver". The screws or other fasteners are joined together in a continuous strip or belt. An automatic feed device is provided to continuously feed the fasteners to the driver. The feed device is actuated when the operator of the driver presses the driver against a workpiece.
A power driver of this type is known from German Patent Publication (DOS) No. 2,452,246, corresponding to U.S. Pat. No. 3,930,297; granted on Jan. 6, 1976. The power screw driver disclosed by this German Publication is provided with a foot with which the driver can be set down on a workpiece. The screws are held in the legs of a U-shaped holding belt which is moved into a recess of a bearing body. During the screwing-in the first screw in a strip is released from the holding belt and screwed into the workpiece. If the screw is released from the holding belt before the point of the screw has penetrated into the workpiece, it is possible for the screw to slant or tip at an angle. If the screw is at a slant it will either go into the workpiece crooked or it will jam. This difficulty can only be avoided if the point of the screw supplied to the driver is located as near as possible to the surface of the workpiece. However, with screws of different lengths the driving spike of the power driver in the rest position must be at least above the head of the longest screw. The disadvantage here is that with shorter screws an unproductive driving movement of the drive spike towards the workpiece is necessary until the drive spike engages in the head of the shorter screw.
From the above it may be seen that the driving stroke is always the same length both with short and long screws. This leads to an inefficient waste of time and energy with the shorter screws. On the other hand, if the screws supplied to the power driver are mounted in such a way that the heads of screws of different length are always located at the same height, then the points of the shorter screws are relatively far away from the workpiece. This gap between screw point and workpiece can mean that the shorter screws will take up a slanting position which leads to jamming or faulty fastening work.
In practice there are unavoidable differences in the lengths of the screws and also in the embedding of the screws in the holding belt. Either of these imperfections can result in the screw being released from the holding belt before the point of the screw has penetrated into the workpiece. Therefore, faulty screwing and jamming has always been a possibility with the prior art devices.
Attempts have been made to supply screws to the driver in such a way that their points are always located in the immediate vicinity of the surface of the workpiece. One method of doing this is to attach the screws very exactly to the holding belt. However, the high demands for accuracy in the manufacture of the holding belt and the insertion of screws onto the belt results in an increase in the costs of the production of the belt.